Non-target screening of toxic contaminants in secondary effluents (from several sources) using SPE-LC-Orbitrap mass spectrometry.

Toxic contaminants are widely present in aquatic environments; however, many contaminants cannot be eliminated during wastewater treatment. The identification of these contaminants using traditional targeted methods requires considerable effort, time, and specialized reference standards. In this study, a non-target screening method was developed. Samples were analyzed using ultra-high-performance liquid chromatography-Q Exactive Orbitrap mass spectrometry (UHPLC-Q Exactive Orbitrap MS). Data were processed through the small molecule screening software Compound Discoverer 3.3, and the identified toxic contaminants were ranked according to certain scoring rules. The pollutant ranking rules in this study primarily consider the software matching results, detection frequencies, and relative peak areas of detected contaminants. Each maximum value is assigned 100 points, with the remaining points distributed proportionally. The characteristics of contaminants in secondary effluents from individual locations were evaluated to identify surrogate parameters for the detected contaminants. These parameters were used to propose a list of potentially toxic contaminants (PTCs). A total of 229 PTCs, including pesticides, plasticizers, and pharmaceutical and personal care products (PPCPs), were identified in effluent streams from eight wastewater treatment plants (WWTPs) in China. The number of PTCs detected in the secondary effluent positively correlated with several surrogate parameters, including pH, total organic carbon content, excitation emission matrix (EEM), and others, with EEM displaying the strongest correlation. A computational toxicity assessment indicated that these potential priority contaminants are highly toxic, genotoxic, and mutagenic to Daphnia magna.